Are yellow-fleshed potatoes healthier than white? And what about the glycoalkaloid toxins?
The high glycemic impact of potatoes may increase the risk of type 2 diabetes, perhaps by chronically overstimulating the insulin-producing cells in the pancreas. In my last two blogs, I explained how you can decrease the glycemic impact of white potatoes by eating them cold, chilling then reheating them, or adding broccoli, lemon juice, or vinegar. What else can we do?
Well, the pigments in brightly colored berries can act as starch blockers, as you can see below and at 0:38 in my video The Healthiest Type of Potato.
So, if you’re going to eat a high glycemic food, you may be able to moderate its impact by, for example, spreading raspberries on your toast, adding strawberries to your cornflakes, or sprinkling blueberries into your pancake batter. I’m not saying you have to put blackberries in your baked potato, but given that the natural color compounds in fruits can slow down starch digestion, what about pigmented potatoes?
Even regular yellow potatoes like Yukon gold may be preferable to white, but the best may be purple potatoes—not just purple-skinned potatoes but purple-fleshed potatoes. If you’ve never seen purple potatoes, they are remarkable—they have almost a neon-blue glow, which you can see below and at 1:14 in my video.
And not only do they look cool, but purple potatoes cause less of an insulin spike and less of a blood sugar spike compared to even the yellow-fleshed potatoes, suggesting that switching from yellow or white potatoes to purple ones “could have large potential in maintaining public health.”
How do we know the pigments themselves are responsible, rather than other differences between the different potato varieties? Researchers tried using a control made of berries in a potato starch jelly, but that approach would seem to add even more variables. In a test tube, extracts of purple- and red-fleshed potatoes can act as starch blockers. So, if you extract and purify the purple potato pigments, you could remove any other effects of the different potato varieties by adding those purple pigments to yellow potatoes. And lo and behold, compared to plain yellow potatoes, this results in suppressions of blood sugar and insulin spikes. Instead of an overshoot reaction, where blood sugars can actually drop below fasting levels, you get the gentler rise and fall in blood sugars you’d expect from a lower glycemic food, as you can see below and at 2:25 in my video.
The authors suggest purple potato extracts could be produced to make supplements or fancy functional foods, but it might be more cost-effective to get these compounds from consuming purple potatoes themselves.
The purple potato pigments may also affect inflammation. The Potato Association of America likes to paint potatoes as an anti-inflammatory food, but what it doesn’t tell you is that this benefit may be limited to pigmented potatoes. When study participants were randomized to eat a small white potato every day for six weeks versus a yellow- or purple-fleshed potato, those in the purple potato group achieved significantly lower levels of inflammation compared to those in the white potato group, measuring both C-reactive protein and interleukin-6, shown below and at 3:13 in my video.
Pigmented potato consumption also alters oxidative stress. Within hours of eating a large purple potato, you get a nice 60% bump in the antioxidant power of your bloodstream, and this translates into less free radical DNA damage. If you compare the antioxidant activity of white potatoes, yellow potatoes, and purple potatoes, Yukon gold has about twice the antioxidant power as white, but purple has 20 times the antioxidants. That’s comparable to what you might see in berries. Half a purple potato has about the same polyphenol antioxidant content as half a cup of blueberries.
Purple potatoes can increase the antioxidant capacity of our bloodstream, whereas straight white potato starch can act as a pro-oxidant and decrease it. Eat a purple potato, and, over the next eight hours, the antioxidant capacity of your bloodstream goes up. In contrast, if you eat white potato starch devoid of any pigment, you can end up worse off than where you started, as you can see below and at 4:12 in my video.
Okay, but does this translate into different physiological effects? Yes, indeed. When people ate either purple potatoes or white potatoes for two weeks, the purple potatoes improved a measure of arterial stiffness, whereas the white potatoes did not. And this translates into a drop in blood pressure, even in those already taking high blood pressure drugs, suggesting purple potatoes are an effective blood pressure–lowering agent.
But what about the toxic glycoalkaloid compounds found in potatoes? The toxic human dose starts around 2 to 5 mg/kg of body weight, and the lethal dose is not too far behind. But the average amount of total glycoalkaloids found in most potatoes, however, is less than 100 mg/kg; so, at the average American weight of 180 pounds, a toxic dose is like four to nine pounds of potatoes. What happens when you approach that amount? It’s possible you can get nausea, vomiting, or diarrhea that could be easily confused with something like gastroenteritis or food poisoning. Some people can start to get sick at just 1.25 mg/kg of body weight or even experience symptoms at 1 mg/kg. That would only be about two pounds of potatoes at the average American weight. It’s also possible that the glycoalkaloids could start accumulating if you eat potatoes day in and day out. But what about those people who go on a fad potato diet and eat three or four pounds a day? They can do that without risking getting sick if they peel their potatoes, which removes nearly all of the glycoalkaloids.
Doctor’s Note
This is the last in a five-video series on potatoes. If you missed any of the others, see:
You may also be interested in The Best Way to Cook Sweet Potatoes.
The video on berries I mentioned is Getting Starch to Take the Path of Most Resistance.
